1. Technical Field
The present invention relates to an industrial robot comprising a drive shaft provided with a brake unit.
2. Description of Related Art
FIG. 9 is a side view of a common industrial robot. An industrial robot 100 as illustrated in FIG. 9 is a 6-axis vertically articulated robot, which includes six drive shafts J1 to J6. A hand 102 for holding or placing a workpiece W is attached to the tip of a robot arm 101. By appropriately driving the six drive shafts, the hand 102 is moved to a desired position, thereby carrying the workpiece W.
FIG. 10 is an enlarged view of one drive shaft J3 illustrated in FIG. 9. In the drive shaft J3 illustrated in FIG. 10, a plurality of gears 1 to 4 and a reduction gear 5 are arranged between a servomotor 9 and the robot arm 101. The servomotor 9 is composed of a motor body 8 and a brake unit 7 integral with the motor body 8.
When the robot 100 is operated, position control is performed by driving the motor body 8 while releasing the brake unit 7. When the robot 100 needs to be urgently stopped, for example, in the case of risk avoidance, a power outage, or a failure, the drive shaft J3 is braked by using the brake unit 7.
In FIG. 9, one brake unit 7 is incorporated in the servomotor 9. In Japanese Laid-open Patent Publication No. 2009-95939, one brake unit and one additional brake unit are serially incorporated in a servomotor, thereby increasing a braking force.
However, when the brake unit 7 itself does not work in a conventional art, a robot 100 cannot be safely braked. In such a case, as illustrated in FIG. 9, the robot arm 101 rotates around a drive shaft J3 downward due to gravity. This may damage peripherals due to the weight of the robot arm 101 or may damage peripherals when a workpiece W slides from a handpiece 102.
In the configuration disclosed in Japanese Laid-open Patent Publication No. 2009-95939, an additional brake unit is arranged to cut in a power transmission path for a drive shaft. For this reason, even in cases in which an additional brake unit needs to be removed when the additional brake unit does not work or when the additional brake unit is not necessary, a robot cannot be driven in a state in which the additional brake unit is removed. Moreover, a replacement work of the additional brake unit is complicated.
Two brake units can be incorporated in the servomotor. However, in this case, the servomotor has a special structure, which increases the cost of the servomotor. Further, when one of the two brake units does not work, the one brake unit alone cannot be replaced.
The present invention has been made under such circumstances, and an object of the present invention is to provide a safe industrial robot to which an easily replaceable brake unit is additionally attached without cutting in a power transmission path.